Extreme weather events are increasing in frequency, causing disruption to global ecosystems. Large-scale events, such as marine heatwaves, can impact the abundance of prey species, which consequently influences the behaviour of top-level predators such as seabirds. The short-tailed shearwater Ardenna tenuirostris is a trans-hemispheric migrant with typically a highly synchronous breeding phenology. Here, we document short-tailed shearwater colony occupancy for the period 2011-2020, with a focussed assessment of their breeding success in the 2019/20 season, which followed a marine heatwave that occurred predominantly in the non-breeding areas in the North Pacific Ocean. The return of the birds to their breeding colonies in southeast Australia was delayed by approximately 2 wk in October 2019, and the subsequent breeding season ended with only 34% breeding success, with nest abandonment beginning in the incubation phase. A North Pacific marine heatwave in 2019, associated with a mass mortality event of over 9000 birds (‘wreck’ of beach-washed birds), led to reduced adult body condition and carry-over effects causing egg and chick failures during the subsequent breeding season. Localised weather events (i.e. flooding of burrows due to heavy rainfall) also influenced breeding outcomes of the 2019/20 season. The relationship between wreck events and seabird breeding ecology is an understudied area, partly due to the difficulties around quantifying the scale of wrecks. Our study is one of few that documents poor seabird breeding success following the extreme marine conditions which have persisted in the North Pacific Ocean since 2013.

There is an absence of quantitative criteria and definitions for unusual or anomalous mortality events involving birds, often referred to as “wrecks”. These events most commonly involve seabirds, although terrestrial bird wrecks have also been documented. Typically, the peer-reviewed literature investigating wreck events lacks the details necessary to further our understanding of the circumstances and potential causes of these events. This study reviewed the peer-reviewed literature for wrecks involving Ardenna seabirds (shearwaters), and included grey literature and data collected by citizen science (community) groups. Our results showed a significant time-lag between wreck events and when the data was published in the peer-reviewed literature, which did not occur in the grey literature. Both the grey and peer-reviewed literature were often skewed towards reporting larger wreck events, with only the citizen science dataset capturing smaller wrecks. We outline a proposed framework for reporting mortality events, including the use of quantitative categories to document the numbers of birds involved and taxon-specific thresholds. In doing so, we aim to establish a framework to aid in the quantitative reporting and analyses of future seabird wrecks.